Amino hydroxy pyrazines, chlorination

Ring substituents of pyrazine A-oxides show increased reactivity, and substituents in the a-position to the A7-oxide function are more reactive than those in the /3-position. Thus, 2-chloropyrazine 1-oxide is converted into the 2-hydroxy-1-oxide on mild alkali treatment,398 but attempts to carry out a similar reaction with the 2-chIoro-4-oxide were not successful.412 Ammonolysis of the 2-chloro-4-oxide has been achieved, and nitrous acid treatment of the resulting 2-amino-4-oxide gives 2-hydroxypyrazine 4-oxide (Scheme 46). The chlorine atom of both isomeric 2-chloropyrazine A-oxides is readily displaced with sulfanilamide to give the corresponding sulfanilamidopyrazine A-oxides.413,414... 

The 3-amino substituent of various [l,2,4]triazoIo[4,3-a]pyrazines can be acylated (69JCS(C)1593) but it is inert towards normal diazotization procedures (68JHC485). The 3-hydroxy compound could not be chlorinated with phosphorus oxychloride and in the IR spectrum it appeared to exist in both the keto and enol forms (68JHC485). 

Bromo-3-hydroxy-5,6-dimethylpyrazine and 2-bromo-5-hydroxy-3,6-diphenyl-pyrazine with phosphoryl chloride afforded 2,3-dichloro-5,6-dimethylpyrazine and 2,5-dichloro-3,6-diphenylpyrazine, respectively (817) and the bromo substituent in 2-amino-3-bromo-5,6-dimethylpyrazine and its p-aminobenzenesulfonyl derivative have been replaced by chlorine on treatment with aqueous hydrochloric acid in ethanol (812). 

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